The present invention relates to the general technical field of imaging devices allowing the study of samples, notably in the near field or in the far field.
The worldwide development of nanosciences and of nanotechnologies generates research efforts setting into play nanostructures of increasing complexity, in order to give them diverse and varied novel functionalities. This induces the requirement for developing novel characterization (size, structure, optical properties, thermal properties, etc.) and control devices and methods for nano-objects, such as nanoparticles for designing novel materials. Within the scope of the present description of the invention, by “nano-object” is meant a body for which at least one of the dimensions (length, diameter, thickness) is of the order of one nanometer, i.e. less than 100 nanometers and preferentially less than 50 nanometers.
The optical viewing devices—such as optical microscopes—remain attractive because of their flexibility. Such devices conventionally include:                a source of light for illuminating an object to be studied,        a detector for detecting the light emitted by the source.However, these optical devices are presently limited in resolution, notably for viewing objects for which one of the dimensions is less than one half-wavelength of the light emitted by the source. Indeed, when an object has a dimension of less than one half-wavelength of the light which illuminates it, the light is scattered as a spot. It is therefore not possible to obtain a sharp image of the studied object. This fundamental limitation is due to the fact that detection and measurement of the electromagnetic field are achieved at a distance of the order of several wavelengths from the studied object.        
Now, two regions in which are found electromagnetic fields of different natures have to be distinguished:                the first region, located at a distance greater than several times the wavelength of the illumination light is said to be a “far field area”; the electromagnetic field which may be measured in the far field area is formed with so-called “propagative” waves,        the second region which is confined in the vicinity of the surface of the studied object is a so-called “near field area”; the electromagnetic field which may be measured in the near field area is formed by the propagative waves mentioned earlier, associated with so-called “evanescent” waves which are too strongly attenuated for being detectable further away, in other words, the waves decrease exponentially with distance and are only detectable in the vicinity of the surface of the studied object.In order to attempt to get over resolution limit, it is possible to resort to other excitation modes of the studied object in other ranges of frequencies (wavelengths).        
An object of the present invention is to propose in the microwave range an imaging device similar to the one allowing characterization and control of an object, such as a nano-object, in optics. Such a device may also be advantageously utilized in microwaves for non-destructive evaluation of macro-objects consisting of various materials, either manufactured materials such as dielectrics or composites, or natural materials like wood.